Mercury Calibration System
U.S. Environmental Protection Agency (EPA) Performance Specification 12 in the Clean Air Mercury Rule (CAMR) states that a mercury CEM must be calibrated with National Institute for Standards and Technology (NIST)-traceable standards. In early 2009, a NIST traceable standard for elemental mercury CEM calibration still does not exist. Despite the vacature of CAMR by a Federal appeals court in early 2008, a NIST traceable standard is still needed for whatever regulation is implemented in the future. Thermo Fisher is a major vendor providing complete integrated mercury continuous emissions monitoring (CEM) systems to the industry. WRI is participating with EPA, EPRI, NIST, and Thermo Fisher towards the development of the criteria that will be used in the traceability protocols to be issued by EPA. An initial draft of an elemental mercury calibration traceability protocol was distributed for comment to the participating research groups and vendors on a limited basis in early May 2007. In August 2007, EPA issued an interim traceability protocol for elemental mercury calibrators. Various working drafts of the new interim traceability protocols were distributed in late 2008 and early 2009 to participants in the Mercury Standards Working Committee project. The protocols include sections on qualification and certification. The qualification section describes in general terms tests that must be conducted by the calibrator vendors to demonstrate that their calibration equipment meets the minimum requirements to be established by EPA for use in CAMR monitoring. Variables to be examined include linearity, ambient temperature, back pressure, ambient pressure, line voltage, and effects of shipping. None of the procedures were described in detail in the draft interim documents; however they describe what EPA would like to eventually develop. WRI is providing the data and results to EPA for use in developing revised experimental procedures and realistic acceptance criteria based on actual capabilities of the current calibration technology. As part of the current effort, WRI worked with Thermo Fisher elemental mercury calibrator units to conduct qualification experiments to demonstrate their performance characteristics under a variety of conditions and to demonstrate that they qualify for use in the CEM calibration program. Monitoring of speciated mercury is another concern of this research. The mercury emissions from coal-fired power plants are comprised of both elemental and oxidized mercury. Current CEM analyzers are designed to measure elemental mercury only. Oxidized mercury must first be converted to elemental mercury prior to entering the analyzer inlet in order to be measured. CEM systems must demonstrate the ability to measure both elemental and oxidized mercury. This requires the use of oxidized mercury generators with an efficient conversion of the oxidized mercury to elemental mercury. There are currently two basic types of mercuric chloride (HgCl{sub 2}) generators used for this purpose. One is an evaporative HgCl{sub 2} generator, which produces gas standards of known concentration by vaporization of aqueous HgCl{sub 2} solutions and quantitative mixing with a diluent carrier gas. The other is a device that converts the output from an elemental Hg generator to HgCl{sub 2} by means of a chemical reaction with chlorine gas. The Thermo Fisher oxidizer system involves reaction of elemental mercury vapor with chlorine gas at an elevated temperature. The draft interim protocol for oxidized mercury units involving reaction with chlorine gas requires the vendors to demonstrate high efficiency of oxidation of an elemental mercury stream from an elemental mercury vapor generator. The Thermo Fisher oxidizer unit is designed to operate at the power plant stack at the probe outlet. Following oxidation of elemental mercury from reaction with chlorine gas, a high temperature module reduces the mercuric chloride back to elemental mercury. WRI conducted work with a custom laboratory configured stand-alone oxidized mercury generator unit provided by Thermo Fisher to perform experiments to demonstrate the high efficiency of oxidation on reaction with chlorine gas, and reduction back to elemental mercury.
- Research Organization:
- Univ. of Wyoming, Laramie, WY (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-98FT40323
- OSTI ID:
- 993821
- Country of Publication:
- United States
- Language:
- English
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